Methyl methacrylate polymer coating composition



United States Patent METHYL METHACRYLATE POLYMER COAT ING COMPOSITION No Drawing. Application June 4, 1954 Serial No. 434,661

8 Claims. (Cl. 260-30.6)

This invention relates to liquid coating compositions containing polymers of methyl methacrylate and particularly to liquid coating compositions containing polymers of methyl methacrylate having specific viscosity characteristics.

By the term polymer of methyl methacrylate and related terms, as used herein, are meant homopolymers of methyl methacrylate, copolymers of methyl methacrylate and other materials copolymerizable therewith containing at least about 95% by weight of polymerized methyl methacrylate, or mixtures of such homopolymers and/or copolymers.

Coating compositions containing a polymer of methyl methacrylate as the principal film-forming constituent have long been known, but these have not resulted in satisfactory finishes because they had too high viscosity or were too low in polymer content to produce thick films, or they were deficient in essential film properties.

We have found that it is possible to make coating compositions which are free of these objections and which have an especially desirable balance of properties with respect to viscosity, polymer content and filrn properties, by using a particular type of methyl methacrylate polymer which has previously not been used for such a purpose.

Accordingly, it is a broad object of this invention to provide new methyl methacrylate polymer coating compositions rather than to provide improvements in known methyl methacrylate polymer coating compositions.

It is a specific object of this invention to provide coating compositions containing polymers of methyl meth'acrylate, which polymers have not previously been em-. ployed for any practical purpose and, in particular, not asfilm-forming materials in coating compositions.

These objects are accomplished by employing a particular type of methyl methacrylate polymer, i. e., one having a relative viscosity between 1.117 and 1.196, inclusive, as measured by the method described in detail hereinafter.

More specifically, these objects are accomplished 'by 2,934,509 Patented Apr. 26, 1 960 of 1.117-1.196 and solvent therefor, with or without plasticizer and/ or pigment.

The polymers of methyl methacrylate having relative viscosities between 1.117 and 1.196 which are employed in this invention may be selected directly from the products of bulk, granular, emulsion or solution polymerization of methyl methacrylate, with or without up to 5% by weight of other materials copolymerized therewith; i. e., these direct polymerization products are not further processed in any manner which materially affects polymer viscosity. Alternatively, higher viscosity methyl methacrylate polymers, comprising a plurality of fractions having different relative viscosities, one of which fractions has a relative viscosity between 1.117 and 1.196, may be treated by preferential solvency techniques to extract a fraction having the desired viscosity.

JThis invention is not intended to include coating compositions made from higher viscosity methyl methacrylate polymers which are reduced in-viscosity by strenuous milling, as on a rubber mill under conditions of high shear; such compositions being separately disclosed and claimed in copending application Serial No. 192,152,

which was filed October 25, 1950, by Laverne W. Crisseytheir commercial acceptance for use on thin deformable metal, such as is used in automobile bodies.

Methyl methacrylate polymer coating compositions in which the polymer has a relative viscosity above about 1.196 are too high in viscosity to be applied conveniently, or too low in polymer content, at an applicable viscosity, to produce reasonably thick films. Thus they possess the deficiencies of the methyl methacrylate polymer coating compositions disclosed in the prior art, and consequently are not intended to form a part of this invention. One specific method of preparing suitable polymers of methyl methacrylate is by introducing suitable proportions of distilled methyl methacrylate monomer, catalyst and solvent into a closed reaction vessel equipped with a thermometer, agitator and reflux condenser, heating the contents with continuous agitation for about 2 to 9 hours, and then cooling to room temperature.

By using this method under a variety of conditions, as indicated in the following table, methyl methacrylate poly- 1 mers having the relative viscosities required in this inyention are obtained. All ingredients are shown by v weight.

TABLE 1,-ME1HYL METHAOBYLATE POLYMERS Methyl Solvent Percent Reaction Relative Viscosity Molecular Meth- Catalyst Temp., Convcr- Time, Weight acrylate 0. 81011 to Hours Toluene Acetone Polymer 40 V 42 18 0.6 azo 1 130 72 9 40 42 18 0.362 benzoyl peroxide 90 93 9 40 42 18 0.28 are 1 130 9 50' 8 42 0.3025 benzoyl peroxide 92 99 6 40 60 0.306 benzoyl peroxide 94 6 50 35 16 0.2813 benzoyl peroxide 92 99 6 60 8 42 0.27 benzoyl peroxide -89 96 6 45 38. 5 16. 6 0.2417 benzoyl peroxide 89 98 8 66. 67 23. 33 10.0 0.4 benzoyl peroxide 100 98 2 62' 26. 6 11. 4 0.341 benzoyl peroxide 90 3 66. 67 23. 33 10.0 0.333 benzoyl peroxide 96 2 1 A20 catalyst=alpha alpha azodilsobutyronitrile.

providing liquid coating compositions comprising a poly; mer of methyl methacrylate having a relative viscosity Further variations will be obvious to those skilled in the art, such as substituting methyl methacrylate monomer Other polymers of methyl methacrylate may be made in a similar manner.

The relative viscosity values, as employed in the description of this invention and in the appended claims, are the values of the fraction (A) Efflux time of polymer solution (B) Efllux time of solvent used in polymer solution The effiux times are measured in accordance with the procedure of ASTM-D-44546T Method B using, as the oil mentioned in said procedure, (A) a solution of 0.25 gram of the methyl methacrylate polymer being tested in 50 cc. of ethylene dichloride, and (B) a sample of the ethylene dichloride used in making said solution, respectively. The determinations are run at 25 C. in a modified Ostwald viscosimeter, series 50.

By this method the methyl methacrylate polymers employed in this invention have relative viscosity values between 1.117 and 1.196, which correspond to calculated molecular Weight values of 55,000 and 105,000, respectively.

Molecular Weight values, referred to herein, are on the basis of weight average molecular weight, and are calculated from the equation but not by way of limitation. Unless otherwise indicated, the parts and percentages are by weight.

Examples A series of coating compositions of this invention were prepared by grinding pigment, methyl methacrylate polymer, plasticizer and solvent in conventional paint grinding apparatus until smooth dispersions were produced. The proportions and other variables are recorded in the following table:

was accelerated by heating for 30 minutesat 200 F. The resulting coatings were between 1 and 2 mils thick and were glossy, smooth and hard. The coatings were also found to be adherent when scraped with a sharp knife, and flexible when bent through a angle or dented with a spherical impact tester.

Example 10 The following is a formula for a coating composition of this invention which contains a copolymer of methyl methacrylate:

Parts by weight Methyl methacrylate polymer (relative viscosity The methyl methacrylate copolymer contained 98% polymerized methyl methacrylate and 2% polymerized methacrylic acid.

A coating of this composition was similar in appearance and physical properties to the products of Examples 1-9.

Although methyl methacrylate homopolymers, which are a preferred embodiment of the invention, were employed in Examples 'l-9 for purposes of direct comparison, and a 98% polymerized methyl methacrylate/2% polymerized methacrylic acid copolymer was employed in Example 10, other copolymers of methyl methacrylate and other materials copolymerizable therewith, containing at least about by weight of polymerized methyl methacrylate, may be substituted for all or part of the homopolymers used in the above examples, or in other coating compositions within the scope of the appended claims, provided the relative viscosity of said copolymer is between 1.117 and 1.196.

Examples of suitable monomers which can be copolymerized with methyl methacrylate to provide copolymers for use in this invention include acrylic and methacrylic acids, short chain (i.e. 1-4 carbon atom) alkyl esters of acrylic acid, 2-4 carbon atom alkyl esters of methacrylic acid, vinyl acetate, acrylonitrile, and styrene. A particularly preferred copolymer is that employed in Example 10, which contains about 98% methyl methacrylate and 2% methacrylie acid. Mixtures of polymers of methyl methacrylate may also be employed in this invention.

TABLE 2 Example No 1 2 i 3 4 5 6 7 8 9 Methyl Methacrylate Polymer-Relative viscosity-- 1.131 1.133 1.154 1.163 1.183 1.193 1.193 1.193 1.193

Parts by weight:

Methyl methacrylate polymer 15. 5 17. 5 15.0 14. 3 12. 8 12. 3 18.1 12. 3 13. 6 Dibntyl phthalate plastieizer 6. 2 7. 0 6. 0 5. 7, 5. 1 4. 9 5. 2 4. 9 5. 4 Toluene 37. 3 35. 7 37. 7 38. 3 79. 0 39. 9 39. 9 39. 3 39. 7 Xylene 37. 3 35. 6 37. 7 38. 3 40. 0 40. 0 39. 2 39. 8 Titanium dioxide pigment. 3. 7 4. 2 3. 6 3. 4 3. 1 2. 9 Phthalocyanine green pigment" i 1. 8 Milori blue p Em cut 4. 3 Carbon black pigment v p 1. 5 1,00 0 100. 0 100. 0 100. 0 100. 0 100. 0 100.0 100. 0 100. 0

The methyl methacrylate polymer in each example was a homopolymer. Those used in Examples 1, 4, 5, 6, 7, 8 and 9 were prepared in the form of granules by emulsion polymerization in Water, and those used in Examples 2' and 3 were preparedby solution polymerization in toluene.

The resulting coating compositions were applied by conventional methods to steel panels which had been preiou ly p med w h a a e c a g of a nven ion l The preferred polymers have relative viscosities between 1.148 and 1.183.

Although toluene and xylene were employed as the solvents in the above examples for purposes of illustration, the invention is not limited thereto. Other solvents for the polymers of methyl methacrylate employed in this invention may be substituted for all or part of the solvents used in the examples. Other suitable solvents in-vv clusleketone such as acetone, esters such asv ethyl ace! metal primer. The drying of the newly-applied coatings 76 tate, ether alcohols such as ethylene glycol monoethyl ether, and aromatic hydrocarbons such as benzene. Nonsolvents, such as alcohols and aliphatic hydrocarbons, may be employed provided suflicient solvent is present to dissolve the polymer....

Therelative amounts of polymer and solvent which may beused is not critical, and is limited entirely by the practical considerations of suitable application viscosity and suitable thickness of the coating. Dilute solutions of low viscosity polymers are one extreme and produce only very thin coatings under practical conditions. Converse- 1y, concentrated solutions of high viscosity polymers are diflicult to apply in the form of uniform coatings. The most useful concentrations are %-50% by weight of polymer based on the total weight of polymer and solvent. In the lower portion of this range, the preferred polymers are of relatively high viscosity, and in the upper portion of this range the preferral polymers are of relatively low viscosity, thus providing easily applied compositions which yield relatively thick coatings.

Many well-known plasticizers for polymers of methyl methacrylate may be employed in the compositions of this invention to replace all or part of the dibutyl phthalate or benzyl butyl phthalate used in the examples. However, the particular plasticizer used affects the physical properties of the resulting coating, including, for example, cracking, crazing, flexiblity and durability. The other preferred plasticizers which will produce films having especially desirable properties, are triphenyl phosphate, 2-ethyl hexyl benzyl phthalate and dicyclohexyl phthalate. Other well-known plasticizers for polymers of methyl methacrylate which may be employed include diallyl phthalate, dibenzyl phthalate, butyl cyclohexyl phthalate,

mixed benzoic acid and fatty oil acid esters of pentaery- I thritol, poly (propylene adipate) dibenzoate, diethylene glycol dibenzoate, tetrabutylthiodisuccinate, butyl phthalyl butyl glycolate, acetyl tlibutyl citrate, dibenzyl sebacate, tricresyl phosphate, toluene ethyl sulfonamide, the di 2- ethyl hexyl ester of hexamethylene diphthalate, and di- (methyl-cyclohexyl) phthalate. Plasticizers are normally employed in amounts of about 10-50% by weight based on the weight of the polymer of methyl methacryl ate.

In place of or in addition to the pigments disclosed in the examples, a wide variety of other pigments commonly used in organic coating compositions may be used. Examples of such other pigments include other iron blues, such as Prussian blue or Chinese blue, phthalocyanine blues; metal oxides, hydroxides, sulfides, sulfates, silicates and chromates; organic maroons, aluminum flake, bronze powders, pearl essence, and various fillers or extenders such as talc, barytes, china clay and diatomaceous earth. Mixtures of such pigments may also be used.

It will be obvious to those skilled in the organic coating art that the amount of pigment used is not critical, except that it must be high enough to provide the necessary hiding power. The amount of pigment, by weight based on the weight of the organic film-fonning material, may vary between about 2% for light, high-hiding pigments, such as carbon black or aluminum, and about 100% for heavy, low-hiding pigments such as lead chromate.

Pigments may be omitted from the compositions of this invention to provide clear coating compositions.

The method of dispersing or grinding pigment in the film-forming materials is not critical provided a smooth, uniform dispersion of finely divided pigment is produced. Examples of suitable equipment well-known in the art are ball, pebble, buhrstone, roller, and colloid mills, and kneader-mixers, such as Banbury or Werner-Pfleiderer. The pigment may be ground with all of the other ingredients or only part of them. In the latter case the balance will be admixed after the grinding is completed.

While the preferred coating compositions of this invention contain, as film-forming materials, only polymers of methyl methacrylate and plasticizers therefor, suitable compositions may be'prepared by incorporating other compatible film-forming materials with the aforemen tioned ingredients in proportions up to about 10% by weight based on the total weight of the film-forming c'onstituents of the composition. Examples of such additive film-forming materials are cellulose nitrate, other cellulose esters, alkyd resins, and polymers of the short chain alkyl esters of acrylic and methacrylic acids other than polymethyl methacrylate. Obviously it is most convenient to incorporate the additive materials in the form of solutions.

While the examples show baking as a step in the preparation of coatings from the products of this invention, the baking step is not essential. Baking is mainly a means of shortening the drying period to a If desired, the coatings may be air dried under normal conditions of atmospheric temperature and humidity with good ventilation. Air drying to a stage which permits handling usually requires 4-24 hours. Baking at 150- 200 F. normally reduces the drying time to 30-60 minutes, whereas baking at 250-300 F. reduces the time to 15-20 minutes.

The coating compositions of this invention are useful for applying decorative and protective coatings to articles manufactured from a variety of materials, such as wood, metal, ceramics and other organic and inorganic sub stances. In many cases, such as in coating metal, it may be desirable first to coat the substrate with a suitable priming composition. An important advantage of the resulting coatings is their excellent outdoor durability, as evidenced by retention of their original gloss and resistance to disintegration of the film during prolonged exposure to the elements.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof; and, therefore, it is not intended to be limited except in accordance with the appended claims.

We claim:

1. A coating composition comprising a polymer of methyl methacrylate having a relative viscosity between 1.117 and 1.196 inclusive and a solvent therefor, said polymer of methyl methacrylate being a member of the group consisting of homopolymers of methyl methacrylate, copolymers of methyl methacrylate and another material copolymerizable therewith containing at least about by weight of polymerized methyl methacrylate, said other material being a member of the group consisting of acrylic acid, methacrylic acid, 1-4 carbon atom alkyl esters of acrylic acid, 24 carbon atom alkyl esters of methacrylic acid, vinyl acetate, acrylonitrile and styrene, said polymer being present in the amount of 10% to 50% by weight based on the total of said polymer and solvent.

2. The product of claim 1, in which the polymer of methyl methacrylate is a homopolymer.

3. The composition of claim 1 in which the polymer of methyl methacrylate is a copolymer of methyl methacrylate and acrylic acid, said copolymer containing at least about 95 by weight of polymerized methyl methacrylate.

4. The composition of claim 1 in which the polymer of methyl methacrylate is a copolymer of methyl methacrylate and methacrylic acid, said copolymer containing at least about 95% by weight of polymerized methyl methacrylate.

5. The composition of claim 1 in which the polymer of methyl methacrylate is a copolymer of methyl meth-' acrylate and 1-4 carbon atom alkyl esters of acrylic acid,

said copolymer containing at least about 95 by weight of polymerized methyl methacrylate.

6. The composition of claim 1 in which the polymer of methyl methacrylate is a copolymer of methyl methwe ght of polymerlzed methyl methacrylate. 2,

7. The composition of claim 1 containing a plasticizer of the group consisting of dibutyl phthalate, benzyl bntyl 5 2,063,078 v phthalate, triphenyl phosphate, Z-ethyl hexyl b l 2,204,517

phthalate, and' dicyclohexyl'phthalate. V 2,397 8. The composition of claim 1 containing a pigment. 2,384,070

References Cited in thc filo of patent UNITED STATES PATENTS Strain Iuly'7, 1936 Barrett L. 'Dec."8,1936 Strain Inne 11', 1940' Pearce Nov. 7, 1944 

1. A COATING COMPOSITION COMPRISING A POLYMER OF METHYL METHACRYLATE HAVING A RELATIVE VISCOSITY BETWEEN 1.117 AND 1.196 INCLUSIVE AND A SOLVENT THEREFOR, SAID POLYMER OF METHYL METHACRYLATE BEING A MEMBER OF THE GROUP CONSISTING OF HOMOPOLYMERS OF METHYL METHACRYLATE, COPOLYMERS OF METHYL METHACRYLATE AND ANOTHER MATERIAL COPOLYMERIZABLE THERWITH CONTAINING AT LEAST ABOUT 95% BY WEIGHT OF POLYMERIZED METHYL METHACRYLATE, SAID OTHER MATERIAL BEING A MEMBER OF THE GROUP CONSISTING OF ACRYLIC ACID, METHACRYLIC ACID, 1-4 CARBON ATOM ALKYL ESTERS OF ACRYLIC ACID, 2-4 CARBON ATOM ALKYL ESTERS OF METHACRYLIC ACID, VINYL ACETATE, ACRYLONITRILE AND STYRENE, SAID POLYMER BEING PRESENT IN THE AMOUNT OF 10% TO 50% BY WEIGHT BASED ON THE TOTAL OF SAID POLYMER AND SOLVENT. 